An interesting excerpt: "Take-up of computerised CBT was low, despite regular calls to encourage participants to use the programmes. The median number of sessions completed was two out of eight for Beating the Blues and one out of six for MoodGYM. Only 18% of people who started Beating the Blues completed all modules and 16% for MoodGYM."
Online CBT definitely is not effective if patients don't complete it despite receiving phone calls. I can imagine that getting the motivation to log in and do it is really difficult when you're already feeling hopeless-- even not-depressed people have enough trouble building and sticking to habits as it is.
But I still wonder if online CBT was effective for the small portion of participants who did complete it? What were the characteristics of those who did complete the app? Perhaps we can learn something.
CBT app builders should also consider that self-care options for depression have existed for a long time in the form of books. Can an app do a substantially better job than books? The idea of solving medical issues remotely has been tried for decades.